1. Field of the Invention
The present invention relates to a rechargeable battery, and more particularly to a rechargeable battery including a bare cell having an electrode assembly, a can, and a cap assembly and a protective circuit board electrically coupled to the bare cell.
2. Description of the Prior Art
Rechargeable batteries may be compact in size and still have a large capacity. Typical examples of rechargeable batteries include nickel-metal hydride (Ni—MH) batteries and lithium ion batteries, such as lithium ion polymer batteries.
FIG. 1 is an exploded perspective view showing a conventional can-type lithium ion battery. FIG. 2 is a partial perspective view showing a breaker, a lead plate, and the like, which are installed on a cap plate of a bare cell of the battery shown in FIG. 1 before a protective circuit board is coupled to the bare cell.
Referring to FIG. 1 and FIG. 2, the lithium ion battery may include a bare cell having an electrode assembly 212, an electrolyte, a can 10, and a cap assembly and a protective circuit board 300 coupled to the bare cell to adjust voltage or current during charging and discharging.
The electrode assembly 212 may be formed by laminating a thin plate or film type positive electrode 213, a separator 214, and an negative electrode 215 and rolling up the laminate.
The can 10 may be made of aluminum or aluminum alloy in an approximately rectangular shape. The electrode assembly 212 may be placed into the can 10 via its open top. As such, the can 10 may act as a container of the electrode assembly 212 and an electrolyte.
The cap assembly may be provided with a flat cap plate 110. The cap plate 110 may have a terminal through-hole 111 formed thereon so that an electrode terminal can extend through. The electrode terminal, which may extend through the cap plate 110, may have a tubular gasket 120 arranged on an outer portion to electrically insulate the electrode terminal 130 and the cap plate 110. An insulation plate 140 may be positioned at the center of the lower surface of the cap plate 110 near the terminal through-hole 111. A terminal plate 150 may be positioned on the lower surface of the insulation plate 140.
A positive electrode tab 216 may be drawn from a positive electrode 213 and welded to the lower surface of the cap plate 110. A negative electrode tab 217 may be drawn from a negative electrode 215 and welded to the lower end of the electrode terminal 130.
The electrode assembly 212 may have an insulation case 190 arranged on the upper surface thereof to electrically insulate the electrode assembly 212 from the cap assembly and cover the top of the electrode assembly 212. The insulation case 190 may be made of a high-molecular resin having insulation properties, such as polypropylene. The electrode assembly 212 may have a lead through-hole 191 formed at its center through which the negative electrode tab 217 may extend and an electrolyte through-hole 192 formed on its side. The electrolyte through-hole may be omitted. A through-hole for the positive electrode tab 216 may be arranged next to the lead through-hole 191 for the negative electrode 217.
The cap plate 110 may have an electrolyte injection hole 112 formed on a side thereof. After an electrolyte is injected, a plug 160 may seal the electrolyte injection hole 112.
The periphery of the cap plate 110 may be welded to the lateral wall of the can 10 to couple the cap assembly to the can 10. After the cap assembly is coupled to the can 10, the upper end of the lateral wall of the can 10 may be bent inwards as a flange on the cap plate 110.
The cap plate may have a protrusion formed on a side thereof. A holder 320 may be coupled to the protrusion 310. The holder 320 may have a groove formed at its center so that the protrusion 310 may be inserted and fitted without clearance. Once the holder 320 is fitted to the protrusion 310, the holder 320 will move very little even when subjected to a lateral force. The holder 320 may simply cover the protrusion 310 or may be welded to the holder 320 to improve the strength.
When the holder 320 is welded to the protrusion 310, the holder 320 may be made of the same or similar material as the protrusion 310. The holder 320 increases the height of a structure vertically extending from a horizontal surface of the cap plate 110 even if the protrusion 310 is short. Therefore, a shaped resin portion may be prevented from slipping on the low-profile protrusion and separating from a unit cell, even when a pack battery is subjected to an external twisting force.
The electrode terminal 130 may be arranged at the center of the cap assembly and may protrude from the cap plate 110. The electrode terminal 130 may have a separate tab with conductive properties (not shown) attached to it in a similar manner as that between the protrusion 310 and the holder 320. Although the tab is positioned at the center of the cap plate 110 and has weak resistance to an external twisting force, it can sufficiently act as a support against an external bending force.
The cap assembly may include a cap plate 110 for sealing an opening through which the electrode assembly 212 is placed into the can 10, an electrode terminal 130 insulated from the cap plate by a gasket 120, and a lead plate 410 for electrically coupling the bare cell to the protective circuit board 300. A breaker 420 may be coupled to the cap plate as a battery safety device.
An electrode 217 of the electrode assembly may be welded to a terminal plate 150 inside the bare cell. The terminal plate 150 may be spaced apart from the lower surface of the cap plate 110 by the insulation plate 140 and may be electrically coupled to the electrode terminal 130, which is insulated from the cap plate 110 by the gasket 120. Another electrode 216 of the electrode assembly may be directly welded to a surface of the cap plate 110.
The breaker 420 may be attached to the top of the cap plate 110 and insulated from the cap plate 110 by an insulation material 330, such as double-faced tape. The electrode terminal 130 may be coupled to an electrical terminal 421 formed on a side of the breaker 420. An electrical terminal 423 arranged on the other side of the breaker 420 may be coupled to an electrical terminal 370 of the protective circuit 300. Hereinafter, the electrical terminal 130 of the bare cell will be referred to as an “electrode terminal” and the electrical terminal 421, 423 of the current interruption device will be referred to as an “electrode” so that it may be distinguished from the electrical terminal of the protective circuit board. The lead plate 410 may be welded to a side of the cap plate 110, which is opposite to the breaker 420 about the electrode terminal 130. The lead plate 410 may be coupled to another electrical terminal 360 of the protective circuit board 300. The breaker 420 may be coupled in series between the protective circuit board 300 and the electrode terminal of the bare cell 130 so that charging and discharging current can flow through it. The reference numbers 311 and 321 are external terminals to connect the battery to a charger or electronic devices. A problem with the charging or discharging current may generate heat and increase the temperature. Upon sensing this heat, the breaker 420 may interrupt the circuit.
The breaker 420 is commonly made of a bi-metal switch, which is opened to interrupt the current or closed to allow the current to flow as the temperature rises or falls, respectively. However, this feature may be dangerous because, although the current may be temporarily interrupted when the rechargeable battery malfunctions, the danger may persist and eventually the rechargeable battery may catch fire or explode. Therefore, an irreversible safety device, such as a PTC (positive temperature coefficient) device, may be used instead of the breaker 420.
When a breaker 420 is used as shown in FIG. 1 and FIG. 2, additional cost and space are necessary to provide the breaker 420 with electrodes 421 and 423 to couple the breaker 420 to the electrode terminal 130 and to the electrical terminal 370 of the protective circuit board 300, respectively. For the sake of electrical coupling to the protective circuit board 300, the lead plate 410, the electrical terminals of the breaker 421 and 423, and the electrical terminals 360 and 370 of the protective circuit board 300, all of which are connected to the bare cell, may have an approximately L-shaped configuration. Horizontal portions of the L-shaped terminals may be fixed to the bare cell or to the protective circuit board 300, and the vertical portions thereof may be welded while corresponding parts are overlapped. As a result, the vertical portions may increase the overall length of the rechargeable battery. This is counterproductive to the goal of producing compact rechargeable batteries having a large capacity.
In addition, a separate insulation material, such as double-faced tape, must be prepared and attached to the cap plate to insulate the entire breaker from the cap plate. This requires additional materials and increases manufacturing costs.